The People’s Liberation Army Navy has found a fairly straightforward way to protect one its strategic priorities in the South China Sea, the New York Timesreported today:

The dispute with the Philippines involves a cluster of reefs and rocks, the Scarborough Shoal, which is called Panatag in the Philippines and Huangyan in China. In May, the Obama administration quietly negotiated a deal that called for Filipino and Chinese vessels to leave the shoal.

But the Chinese left behind a rope that still blocks the entrance to the lagoon, said two Asian diplomats familiar with the situation, who declined to be named per diplomatic protocol.

Three Chinese vessels have apparently been left behind to ensure that no Filipino vessels attempt to cut the rope and enter the lagoon. According to a statement in August by the Philippines Defense Minister, it is "a long rope held by buoys at both ends of the entrance to the lagoon of the horseshoe-shaped reef."

It may seem a bit low-tech today, but this is a strategy with a venerable tradition. In the Byzantine era, the city of Constantinople strung a chain across the gulf that divides the city in order to prevent unwanted ships from entering, an impressive feat as the chain would have to have been at least 500 meters long. In the 18th century, Spanish colonists strung a chain across Colombia’s Boca Chica Strait in order to block of the entrance to Cartagena Bay.